Arteriovenous malformations (AVMs) are direct vascular connections between arteries and veins without an intermediate capillary bed. This is a disorder in which the arterial, i.e. oxygen-rich, blood flows out of an artery and drains directly into a vein without the oxygen contained therein being taken up by the tissue. Depending on the size of the AVM, a not inconsiderable volume of blood can be transferred. Whether clinical significance attaches to such a malformation is dependent on the site at which it is located and its size.
Irradiating the site with ionizing radiation, in a similar manner to treatment of a tumor, is used as a method of treating such arteriovenous malformations. The objective in this case is to direct the radiation at the nidus—i.e. the aggregation of vessels between artery and vein—ideally on the arterial inflow side or alternatively on the venous outflow side, wherein it is intended that the other side in each case should receive the minimum possible dose, i.e. should suffer as little damage as possible. Toward that end it is necessary on the one hand to identify the precise location of the nidus and on the other hand also to establish the arterial and venous assignment of the vessels belonging to the nidus.
For optimum localization of the AVM it is usual to carry out a 3D rotation angiography with the aid of a rotatable imaging system, in particular a rotatable imaging system that is embodied for producing a CBCT (cone-beam computed tomography) image, in particular a C-arm system for producing a CBCT image, wherein a multiplicity of projections are recorded from a projection angle range of 180°+fan angle during a contrast agent injection and a three-dimensional image of the vessels filled with contrast agent is recorded in the region of the AVM. In order to assign the feeder and/or draining vessels, a time series comprising projective 2D X-ray photographs is generated in most cases during the uptake of contrast agent with the aid of which the feeder and draining vessels are to be identified. The patient is exposed to an additional dose for this purpose.